The present invention relates to a method of attaching small plastic parts securely in a defined position on compression molded parts consisting substantially of bonded or synthetic resin-bound natural fibers or chips, as used in the production of panelling elements.
Panelling parts, in particular those parts having a reinforcing and bearing function, are produced, among other ways as compression molded parts from compressed fiber composite, such as for example pressboard panels. The fiber composites are inexpensive and relatively lightweight, which is especially advantageous in automobile construction. After compression molding, small plastic parts, for example in the form of fastening elements, are attached to the compression molded parts. Since they must have better moldability and greater stability than the compression molded part, these fastening elements are made from a different material and more expensive than the fiber composite.
The fastening elements are attached by adhesive boding, riveting, clenching, ultrasonic welding or else by friction welding. However, all of these methods involve costly machine technology. In addition, adhesive bonding strength is temperature-dependent and also costly due to the adhesive additionally required. Another technique for attaching the fastening element is by locking the fastening elements on to metal clips which are placed into the compression mold during the compression molding of the compression molded part. This technique has the disadvantage, however, not only of the additional material expenditure but also of the intervention necessary for this in the compression molding cycle.
An object of the present invention is to utilize a method by which small plastic parts can be attached simply and inexpensively to the compression molded part.
That object has been achieved according to the present invention by a direct, form-fitting injection molding of the small plastic part onto the wall of the compression molded part. In a method according to the present invention, after compression molding of the compression molded part, the small plastic parts are molded in place and fastened to the compression molded part in a single working step by an injection molding process. Since the injection molded plastic is used both for fastening and for the plastic parts themselves, there is not only the advantage in terms of time and costs from saving at least one working step, but also the cost advantage from saving the previously required auxiliary materials and substances such as screws, clips or adhesive. Under certain circumstances, less expensive plastics than previously can also be used.